Many of the long established methods and apparatus for melting or smelting said materials require substantial installations which are costly to build, maintain and run; have low thermal efficiency may cause unacceptable atmospheric pollution and, in some cases, are only suited to the handling of higher melting point metals such as iron and steel.
More recently apparatus such as electric induction melting furnaces and vortex melting devices have been developed for lighter and lower melting point metals such as aluminium scrap but again such installations will only operate effectively on a large scale involving substantial capital cost, high energy input, and inability to process small batches of material.
In the case of aluminium can scrap the empty cans are normally first passed through a delacquering process and shredded, and these shreds are then fed into an induction or vortex melter which has to hold a substantial volume of already molten metal because the incoming scrap is only heated to melting point by heat directly conducted to it from the molten bath. If too great a quantity of unmelted material enters the bath it may cool the latter so that it solidifies, thus a large volume of molted metal has to be kept heated. Moreover the shredded scrap tends to float on the surface of the bath so that it fails to melt. To counteract this agitation has to be provided e.g. either by the action of the induction heating current and/or by provision of mechanical agitation as with the impeller of vortex melting plant.
Furthermore excessive oxidation of the melt has to be prevented so that the whole process has to be carried out in a closed system with consequent problems of air locks or other sealing for the entry of the material and the tapping of the melt.
The heat requirements and heat losses are substantial if only because a large bath of metal has to be maintained in a molten state continuously prior to start up and throughout the operation.
The use of disposable aluminium cans, notably for beverages, is becoming more widespread particularly as brands are increasingly promoted nationwide and internationally e.g. on the European market, necessitating transport and distribution throughout wide areas. There is also increasing emphasis on the collection and recycling of can scrap both on economic and environmental grounds. Hitherto can scrap recovery plants have had to be large scale operations with substantial throughput for the reasons stated above so that optimum operation only becomes possible if the scrap is collected from a wide catchment area with consequent transport costs. Small scale plant, e.g. such as might be operated by a local scrap merchant, has not hitherto been practicable.
The same considerations apply to the recycling or recovery of similar scrap aluminum or other metal material, e.g. swarf and chippings or shredded or pulverised scrap from other sources.
The object of the invention is to provide metal melting or smelting apparatus, particularly for aluminium or other scrap recovery, which is particularly efficient and economical in use, can be provided in a wide range of sizes for large or small throughputs and the handling of small or large batches of scrap, which is of low initial cost and easy to install and maintain, and which is environmentally acceptable both in scale and in its manner of operation.